> The software gives me proxies like
> fe80::1d30:5e9b:97e0:9cfa and it seems like it's not
> accepted.

Try enclosing the address in square brackets, e.g.
[fe80::1d30:5e9b:97e0:9cfa], IPV6 address have often to be written in that
way

Always keep in mind that this software has not been updated for a long time,
and so it's most likely unsafe.